1. Field of the Invention
The present invention relates to an apparatus for indexing an angle of rotation of a rotary table and the like having a worm gear mechanism; and a method of assembling the same.
2. Description of the Related Art
In a worm gear mechanism 1 used for a related art apparatus for indexing an angle of rotation of a rotary table and the like, a rotary shaft 2 fixed to a rotary table (not shown) and a worm wheel 4 are joined together fixedly, and a worm 5 is meshed with this worm wheel 4, as shown in FIG. 1. The worm 5 is made integral with a worm shaft 6. The worm shaft 6 is supported rotatably at one end thereof on a taper roller bearing 8 provided on a body 1a of the worm gear mechanism 1, and at the other end thereof on a needle bearing 9. The worm shaft 6 is joined to a connecting shaft 7 via a coupling 3 so that these shafts are in one body, and further to a motor (not shown) via a connecting gear mechanism 11. A motor shaft 13 forming a rotary driving shaft for the motor (not shown) is connected to the gear mechanism 11, and this motor shaft 13 is connected to the worm shaft 6 via a gear train of the gear mechanism 11 and connecting shaft 7.
The worm gear mechanism 1 has a low speed and a high torque, and is capable of driving a rotary table and the like smoothly. However, providing a certain degree of backlash between the meshed portions of the worm 5 and worm wheel 4 is usually necessary and indispensable, and among the gear train of the connecting gear mechanism 11, etc. connected to the motor shaft 13.
When the quantity of such a backlash is set large, the rotational resistance due to the friction of the surfaces of the teeth of the gear occurring during a high-speed rotation of the gears becomes low, and the generation of heat can be restrained. However, when a rotary table is positioned during a low-speed rotation thereof, it is rotated forward and backward. Therefore, every time the direction of rotation of the rotary table is changed, a quantity of play due to the backlash occurs to cause a position indexing accuracy to lower. Moreover, when a work is processed, an external force is applied thereto, and a decrease in a processing accuracy due to the occurrence of a rattle ascribed to the backlash of the gears, and vibration due to the processing operation occur in some cases.
When a backlash is set small for the purpose of increasing the a position indexing accuracy, an increase in the rotational resistance due to the friction of the surfaces of the teeth of the gear during a high-speed rotation of the indexing apparatus, and the generation of heat in and the abrasion of the surfaces of the teeth occur. Consequently, the indexing apparatus cannot be rotated at a high speed, and a processing speed lowers.
Therefore, in order to set the quantity of a backlash of a gear train of a related art worm gear mechanism and other similar mechanism, a suitable level is selected by taking a point of compromise in accordance with the use of the apparatus and from the above-mentioned contradictory points of view. In consequence, an indexing apparatus capable of being rotated at a high speed with a high accuracy have been unavailable.
The invention has been made in view of the above-mentioned circumstances, and provides an indexing apparatus capable of holding down the quantity of backlash, being driven at a high speed with a high accuracy and assembled easily; and a method of assembling the same.
The invention is directed to an indexing apparatus provided with a worm shaft having a worm thereon, a worm wheel meshed with the worm, and a motor for driving the worm shaft, the worm shaft and a shaft of the motor being connected together by a direct connecting method and the like without interposing a rotation transmission mechanism, such as gears, etc. therebetween.
The invention also provides an indexing apparatus in accordance with the above indexing apparatus, in which a body frame supporting the worm wheel thereon rotatably is provided, the worm shaft being supported rotatably at both end portions thereof on bearings, the bearing for one end portion of the worm shaft being provided on the body frame, the bearing provided for a motor shaft-side portion which constitutes the other end portion of the worm shaft being fixed to a bearing fixing portion formed on a retainer member to which the motor is fixed.
The invention further provides a method of assembling such an indexing apparatus, including providing a body frame on which a worm wheel is supported rotatably, and fixing with a worm shaft and a motor shaft in a unitarily connected state the worm shaft to a worm shaft fixing portion of the worm wheel-carrying body frame.
The invention also provides a method of assembling such an indexing apparatus in accordance with the above method, in which the method includes providing bearings around both end portions of the worm shaft, fixing one end portion of the worm shaft with the relative bearing to a bearing fixing portion formed on a retainer member to which a motor is fixed, and fixing the retainer member to the body frame, the worm shaft being thus fixed to the worm shaft fixing portion of the body frame.